Oil platforms may be used in offshore oil and gas production. More recently, processing facilities are being relocated to the ocean floor. Such subsea installations may use electric power to operate. Electric power may be produced subsea or may be transported to the subsea installation from a topside installation (e.g., via an umbilical from an oil platform or ship, or via a subsea cable from an onshore site). Higher voltages may be used for transporting electric energy from the topside installation to the subsea installation (e.g., to limit losses). Accordingly, a transformation to a lower voltage at which subsea equipment is to be operated is to be provided. A transformer may step up a voltage supplied by offshore power generating devices, such as wind turbines, for the transmission to an onshore site. For this purpose, a subsea transformer may be provided at a subsea installation.
The subsea installation may be located at a great water depth (e.g., more that 1000, more than 2000 or even more than 3000 meters deep). The high pressures that prevail at such depths of water may be dealt with by providing a pressure resistant enclosure for the transformer, the inside of which is kept at a close to atmospheric pressure. The problem with such enclosures is that the enclosures are very bulky and heavy, as the enclosures are to withstand pressure differences up to 300 bar.
To overcome such problems, the transformer may be provided in an enclosure that is pressure compensated (e.g., in which the inside pressure is equalized to the outside pressure). The pressure difference may thus be kept small, enabling the use of a lighter enclosure having thinner walls. Although this greatly facilitates the design of the enclosure, a number of problems remain.
To provide a safe operation of the transformer, the transformer enclosure is to be tightly sealed against the ambient sea water. For example, a proper sealing of the enclosure provides that providing pressure compensation may be difficult. The transformer is to be contacted electrically. The electric connections through the enclosure to the transformer are again difficult to seal.
Enclosed volumes that are additionally provided for sealing either are to be provided with thick walls that are capable of withstanding the high outside pressures, or also are to be pressure compensated. Accordingly, pressure compensation of the transformer enclosure is difficult to implement, the pressure compensation may be complex in configuration and may require a considerable amount of space, making the transformer enclosure bulkier. Further, due to the technical complexity, the pressure compensation may be cost intensive to implement. Each pressure compensation furthermore uses sealing that is a potential weak point regarding the water-tightness of the subsea transformer enclosure.
Assembly of the subsea transformer is thus complex and time intensive. It is desirable to facilitate the assembly and to reduce the number of weak points in the sealing of the subsea transformer to prevent the ingress of surrounding sea water. A compact and cost efficient design of the subsea transformer is further desirable.